Abstract:From the UV-Vis absorption spectra, the FT-IR absorption spectra and the Raman spectra, it is deduced that Co ions primarily occupy the tetrahedral (A) site, with a minor number of them entering into the octahedral (B) site in the Ni_1-xCo_xCr₂O₄ compounds. The origin of the position disorder of the Co ions is consistent with the similar ionic radii of the Co ion (0.65 ？) and the Cr ion (0.62 ？) at B site. The FT-IR peak at about 510 cm^-1 shifts towards high frequency side with the increasing cobalt content. It is resulted from the reduction of the cation-oxygen distance in the octahedron by the replacement of the Ni²⁺ with the Co²⁺ ions. The magnetic measurement shows that Curie temperatures (T_C) are 75 and 90 K for the compounds with x=0.2 and 0.8, respectively.

Key words: spinel; antisite defect; electronic transition; optical properties; magnetic properties